Method for detecting and indicating wedge in glass

ABSTRACT

A method of measuring wedge in a glass sheet has the following steps. A beam of parallel light rays is projected through the glass sheet. The beam is reflected through the glass sheet and passes through an adjustable correction device. The correction device controls the direction of further projection of the reflected beam depending on the relative position of the device. The reflected beam is split along an axis into at least two separate beams which, in turn, are projected onto separate lightmeasuring devices. The light-measuring devices produce a signal corresponding to the intensity of the beams projected thereon. The adjustable correction device is repositioned to a position which causes a prescribed relationship to be established in the signals developed by the light-measuring devices. The position of the correction device indicates the direction and degree of wedge in the glass sheet.

United States Patent [72] Inventors Max J, lrland Dearborn; Victor L.Lindberg, Northville, Mich. [21] Appl. No. 865,338 [22] Filed Oct. 10,1969 [45] Patented May 18, 1971 [73] Assignee Ford Motor CompanyDearborn, Mich. Continuation-impart of application Ser. No. 601,437,Dec. 13, 1966, now abandoned.

[54] METHOD FOR DETECTING AND INDICATING WEDGE 1N GLASS 4 Claims, 3Drawing Figs.

[52] US. Cl 356/239, 250/219 [51] Int. Cl G01n 21/32 [50] Field ofSearch 356/239, 120, 161; 250/219 (DF), 219 (TH) [56] References CitedUNITED STATES PATENTS 2,429,066 10/1947 Kuchni 356/161 3/1963 Griss eta]. 356/120 Primary Examiner-Ronald L. Wibert Assistant Examiner-OrvilleB. Chew, Il Attorneys-John R. Faulkner and William E. Johnson ABSTRACT:A method of measuring wedge in a glass sheet has the following steps. Abeam of parallel light rays is projected through the glass sheet. Thebeam is reflected through the glass sheet and passes through anadjustable correction device. The correction device controls thedirection of further projection of the reflected beam depending on therelative position of the device. The reflected beam is split along anaxis into at least two separate beams which, in turn, are projected ontoseparate light-measuring devices. The light-measuring devices produce asignal corresponding to the intensity of the beams projected thereon.The adjustable correction device is repositioned to a position whichcauses a prescribed relationship to be established in the signalsdeveloped by the lightmeasuring devices. The position of the correctiondevice indicates the direction and degree of wedge in the glass sheet.

PATENTEDHAYWIBYI V 3578.869

MAX J. bPl/l/VD Q. Rim w mX ATTORNEYS METHOD FOR DETECTING AND INDICAGWEDGE IN GLASS BACKGROUND AND SUMMARY OF THE INVENTION This inventionrelates to a method for inspecting glass sheets for wedge defects thatmay or may not be readily apparent to an unaided eye. In particular,this invention relates to a method for detecting, measuring andindicating the existence and characterization of wedge in glass sheets.

Wedge is the departure from parallelism between glass surfaces. When aglass sheet contains wedge, any object viewed through the area of wedgeis distorted in shape and its apparent position does not coincideexactly with its actual positron.

In general terms, the method of this invention comprises providing arestricted or point source of light, projecting said light through acollimating lens which converts said light to a plurality of parallelbeams of light and through the glass undergoing test to a mirror. Thelight beams reaching the mirror are reflected by the mirror back throughthe glass undergoing test and through said lens to a light divider whichdivides the now converging reflected light into a first portion and asecond portion. Each such portion is directed through a pair of glasscompensating plates to a roof reflector which divides the portion intopredetermined subportions and diverts the resultant subportions to apair of photocells. The roof reflectors may be positioned in a mannersuch that bisecting planes passing through their roof lines form anangle of 90. With the reflectors in this or optically equivalentalignment for light reception, one such portion is utilized to measurethe horizontal component of wedge while the other portion is utilized tomeasure the vertical component of wedge. Each of the photocells arecomponents of detection systems which are preset in a manner such thatwhen glass without wedge is under inspection the light received by thesephotocells maintains such system in balance. Preferably such balance isobtained when the light is divided equally between such photocells. Whenwedge of the type that causes horizontal deviation of light rays passingtherethrough is present in the glass undergoing test, the deviation oflight beams passing therethrough causes an uneven distribution of lightto the corresponding pair of photocells creating an imbalance in thedetection and correction system of which these photocells arecomponents. This imbalance automatically activates a balancing circuitwhich rotates one of the associated compensating plates until the lightpassing to the associated photocells is returned to present balanceconditions for parallel glass. When vertical wedge is present in theglass undergoing test, the same procedure is effected by the otherportion of the beam issuing from the aforesaid light divider. Themovement required to restore balance in each of the detection units ismeasured both directionally and quantitatively and such measuresutilized as a measure of the pertinent component of wedge. The readingsobtained from such measurement may be utilized to signal and record theexistence and characterization of wedge, mark the location andcharacterization of wedge on the glass, etc.

Other methods of inspecting glass which utilize some of the stepsincluded in the method of this invention are disclosed by Keuhni in U.S.Pat. No. 2,429,066; McMaster et al. in U.S. Pat. No. 2,735,133]; Guntheret al. in U.S. Pat. No. 3,137,756; and Galey et al. in U.S. Pat. No.3,202,043.

The principal object of this invention is to provide a method forinspecting glass sheets and automatically indicating the existence andcharacterization of wedge therein.

BRIEF DESCRIPTION OF THE DRAWINGS More specific objects and advantageswill be apparent from the following detailed description when read inconjunction with the accompanying drawing, wherein:

FIG. 1 is an assembly view of one embodiment of test apparatus which maybe used to carry out the method of this invention;

FIG. 2 is a perspective view of the light divider of FIG. 1 viewed at anangle from the direction of view in FIG. 1; and

FIG. 3 is a cutaway section of the prism shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,particularly to FIG. I, a sheet of glass 11 is shown in position fortesting. A light source 13, e.g. an incandescent lamp, carbon arc,mercury arc, laser, etc., is shown in the upper left of the assembly. Aportion of the light from light source 13 passes through lens 15 and isfocused to pass through pinhole 17in plate 19. The light beam emergingfrom pinhole 17 next passes through filter 21, a sheet of colored glassthat filters out light of unneeded wave length. Such filters arecommercially available and the filter employed here is'chosen to matchthe color sensitivity of the photoreceivers hereinafter mentioned, i.e.the filter permits transmission therethrough of light of wave lengthwhich is efficiently received by the photoreceivers utilized to detectand assist in measuring wedge. After passing through filter 21, thislight beam passes through a prism 23 which turns the light beam anddirects the light beam to collimating lens 25, e.g. an achromat. It willbe understood that a properly positioned mirror can be substituted forprism 23. The light beam upon passing through collimating lens 25 isconverted to a plurality of parallel rays. The lens employed forcollimating in this embodiment had a focal length of about 26 inches.The resultant parallel rays pass through the glass 11 and in suchpassage undergo angle deviation proportional to the degree of wedge andstrike a flat mirror 27.

Lens 25 and mirror 27 are positioned in parallel relationship withrespect to each other and as closely as possible to parallelrelationship with glass ll when it is moved into test position betweenlens 25 and mirror 27.

The pinhole 17 from which the utilized light emerges is positioned fromsuch pinhole and being projected to lens 25 travels a distance betweensuch pinhole and such lens that is essentially equal to the focal lengthof the collimating lens. Within reason, the size of pinhole 17 is notcritical. In this embodiment, the diameter of pinhole 17 wasapproximately onesixteenth inch. A point source of light providingparallel rays can also be obtained by directing a laser beam through apositive lens. The sensitivity of the method for detecting wedge isinversely proportional to the size of the pinhole and directlyproportional to the size and quality of collimating lens. The area oftest is advisedly smaller than the least distance between significantchanges in wedge angle. What constitutes a significant change in wedgeangle is dependent upon the tolerance admissible for the end use. Forglass intended for employment that would merit such checking,significant change would be a change in wedge angle in the range ofabout 20 seconds of arc to about 2 minutes of arc. The instantembodiment as here illustrated was designed to detect changes in wedgeangle of about 1 minute arc.

Mirror 27 may be either a front surface mirror'or a back surface mirror.It is preferably smaller than the collimating lens 25. The smaller ofthe two limits the area of inspection. The light passing through glassIll and striking mirror 27 is reflected back through glass 11 atessentially the same spot as that of its first passage and in returnpassage is again deviated in proportion to the degree of wedge at suchpoint. After passing through glass 11, the reflected beam passes throughcollimating lens 25 and converges toward light divider or beam-splittingmeans 29 which is situated in front of the focal point of such lens.Light divider 29 is more fully illustrated in FIGS. 2 and 3 and herecomprises a beam splitting cube 29-! formed of a pair of matched prismsand a right-angle prism 29-2. The reflected beam is divided by lightdivider 29 into two portions which preferably are quantitatively equal.A first portion of this beam passes directly through light divider 29and thence through compensating plate 31 and compensating plate oradjustable correction device 33 to roof reflector 35. Compensator plate31 and correction device 33 are planeparallel, transparent sheets, e. g.glass.

After passing through correction device 33, the now diverging firstportion beam strikes roof reflector 35 and is divided into twosubportions or subbeams which are respectively diverted to photocells 37and 39. Roof reflector 35 is here rigidly mounted and positioned toequally divide such first beam portion when the glass under measurementis without wedge. Photocells 37 and 39 and the associated circuitry arepreset to receive an equal quantity of light when the glass undermeasurement is without wedge. When glass containing wedge of the typewhich would cause horizontal deviation of light is in test positionbetween lens 25 and mirror 27, the cone of light falling on roof 35 willbe displaced in such a manner that there will be an imbalance inreflected light received by photocells 37 and 39. In operativeelectrical connection with photocells 37 and 39 is a power unit 41 whichincludes a battery, a bridge circuit, and an amplifier. Power unit 41,in turn, is in operative electrical connection with servomotor 43 andwith servomotor 45. Servomotors 43 and 45 are respectively operativelyconnected to compensator or correction device 33 and compensator 31 viashafts 43- 1 and 45-1.

When an imbalance occurs in the reflected light received by photocells37 and 39, it produces an imbalance in the bridge circuit in electricalconnection with such cells causing an electrical signal to betransmitted to the associated amplifier. This signal is amplified andthen actuates servomotor 43 with resultant rotation of shaft 43-1 andcompensator or correction device 33.

The rotation of correction device 33 is in a direction such as todisplace the first, or horizontal deviation indicating, portion of thebeam to its original position thereby restoring balance to theaforementioned bridge circuit. The amount and direction of rotationrequired to return the reception of light on reflector 35 to balance isa measure of the horizontal component of the wedge. Measurement of thedirection and amount of rotation may be made by any suitable means suchas recorder and indicator means 49 and such measurement recorded. Thismeasurement can be utilized to actuate any desired type of signal deviceand to actuate marking means 50 which will mark the glass passingthrough the test area at the location of the wedge. The recording may besynchronized with movement of the glass under test through the test areaand such markings affixed after the glass has moved through the testarea.

Returning to the light divider 29, the remainder of the beam which isidentical in composition to that portion passing directly throughdivider 29 is reflected in an upward direction by beam-splitting cube29-1 striking the reflecting face of prism 29-2 which causes a 90rotation of the beam about its longitudinal axis. This second portion ofthe beam is utilized in identical manner to detect, measure andcharacterize the vertical component of wedge. This second, or verticaldeviation indicating, portion of the beam is thence directedhorizontally and at a 90 angle from the first, or horizontal deviationindicating, portion.

The second portion of the beam after leaving light divider 29 passesthrough compensator 51 and compensator or adjustable correction device53 and falls upon the reflecting surfaces of roof reflector 55.Compensator 51 and adjustable correction device 53 are identical tocompensator 31 and adjustable correction device 33. This portion of thebeam is divided into subbeams by reflectors 55 and directed tophotocells 57 and 59. A plane passing passing through the roof line ofreflector 55 and bisecting the roof angle of 55 forms a 90 angle with aplane passing through the roof line of reflector 35 and bisecting theroof angle of 35. Cells 57 and 59 are in operative electrical connectionwith power unit 61 which includes a battery, a bridge circuit and anamplifier. Power unit 61, in turn, is in operative electrical connectionwith servomotors 63 and 65. Servomotors 63 and 65 are operativelyconnected via shafts 63-1 and 65-1 to compensator 51 and adjustablecorrection device 53. This unit is operated in identical manner with theapparatus 49 and 50 associated with detection, measurement andcharacterization of the horizontal component of wedge. Utilization ofsuch measurement is likewise the same.

Compensators 31 and 51 may also be referred to as zero compensators.When there is no glass in the test area, compensators 31 and 51 arerotated, when necessary, to adjust the beams issuing from light divider29 and striking reflectors 35 and 55 to positions which respectivelyreestablish an equal distribution of the reflected light between thephotocells associated with reflectors 35 and 55. The absence of glass inthe test area is detected by detection means 47, e.g. photodetectionmeans, and the resultant signal is transmitted to power unit 61 which isin electrical connection with power unit 41. The transmission of suchsignal to power units 41 and 61 effects actuation of servomotors 45 and65 and the turning of zero compensators 31 and 51 via shafts 45-1 and65-1 if the corresponding bridge is in a state of imbalance.

In another embodiment, the roof reflectors 35 and 55 and light divider29 are replaced by a pyramid reflector with four associated photocellsserving the same functions as the reflectors and photocells of theillustrated embodiment previously described. ln this embodiment, thepyramid reflector is positioned to reflect a given quantity of light toeach of the four photocells when the glass under test is without wedge.This embodiment also includes a pair of transparent, plane-parallelcompensating plates or adjustable correction devices between the pyramidreflector and the mirror corresponding to mirror 27 of the drawing inthe line of reflection. One such compensating plate or adjustablecorrection device is rotated about a horizontal axis to rebalancedistribution and measure vertical wedge. Another rotates about avertical axis to rebalance reflection distribution and measurehorizontal wedge.

The tenn horizontal wedge as employed herein refers to wedge formed bytwo planes whose projections intersect in a vertical line. Such wedge ina glass sheet will produce horizontal deviation of a light rayapproaching said sheet normal to its face and passing through the areaof wedge.

The term vertical wedge" as employed herein refers to wedge formed bytwo planes whose projections intersect in a horizontal line. Such wedgein a glass sheet will produce vertical deviation of a light rayapproaching said sheet normal to its face and passing through the areaof wedge.

I claim:

1. A method of measuring wedge in a glass sheet which comprises:

generating a beam of parallel light rays;

projecting said beam through said glass sheet;

reflecting said projected beam back through said glass sheet;

passing said reflected beam through a pair of adjustable correctiondevices, each of said devices controlling the direction of furtherprojection of said reflected beam along selected axes depending on thereflected beam along selected axes depending on the relative positionsof said devices;

separating said projected beam into at least four subbeams,

two of said subbeams being representative of the light intensity alongone axis of said reflected beam and two of said subbeams beingrepresentative of the light intensity along a second axis of saidreflected beam, said first and said second axes being respectivelyaligned with the selected axes along which said adjustable controldevices control the projection of said reflected beam;

projecting said first two subbeams onto separate light measuring deviceswhich produce a signal corresponding to the intensity of the beamprojected thereon;

moving said adjustable correction device controlling the projection oflight along said first axis to a position which causes a prescribedrelationship to be established in the signals developed by saidlight-measuring devices measuring said first two subbeams;

projecting'said second two subbeams onto separate light measuringdevices which produce a signal corresponding to the intensity of thebeam projected thereon; and repositioning said adjustable correctiondevice controlling the projection of light along said second axis to aposition which causes a prescribed relationship to be established in thesignals developed by said light-measuring devices measuring said secondtwo subbeams, whereby the position of said adjustable correction devicesindicate the direction and degree of wedge in said glass sheet alongsaid two axes. 2. A method of measuring wedge as defined in claim 1wherein said reflected beam is separated into at least four subbeams by10 axes of said reflected beam are perpendicular to one another.

4. The method of claim 3 wherein said first and said second axes of saidreflected beam are the horizontal and the vertical axes.

1. A method of measuring wedge in a glass sheet which comprises:generating a beam of parallel light rays; projecting said beam throughsaid glass sheet; reflecting said projected beam back through said glasssheet; passing said reflected beam through a pair of adjustablecorrection devices, each of said devices controlling the direction offurther projection of said reflected beam along selected axes dependingon the reflected beam along selected axes depending on the relativepositions of said devices; separating said projected beam into at leastfour subbeams, two of said subbeams being representative of the lightintensity along one axis of said reflected beam and two of said subbeamsbeing representative of the light intensity along a second axis of saidreflected beam, said first and said second axes being respectivelyaligned with the selected axes along which said adjustable controldevices control the projection of said reflected beam; projecting saidfirst two subbeams onto separate light measuring devices which produce asignal corresponding to the intensity of the beam projected thereon;moving said adjustable correction device controlling the projection oflight along said first axis to a position which causes a prescribedrelationship to be established in the signals developed by saidlight-measuring devices measuring said first two subbeams; projectingsaid second two subbeams onto separate light measuring devices whichproduce a signal corresponding to the intensity of the beam projectedthereon; and repositioning said adjustable correction device controllingthe projection of light along said second axis to a position whichcauses a prescribed relationship to be established in the signalsdeveloped by said light-measuring devices measuring said second twosubbeams, whereby the position of said adjustable correction devicesindicate the direction and degree of wedge in said glass sheet alongsaid two axes.
 2. A method of measuring wedge as defined in claim 1wherein said reflected beam is separated into at least four subbeams byinitially splitting said beam into first and second beam portionsrespectively representative of the light intensity along the first andthe second axes of said reflected beam, passing said first and secondbeam portions through associated ones of said adjustable correctiondevices; and splitting said first and said second beam portions intosaid first subbeams and into said second subbeams.
 3. The method ofclaim 2 wherein said first and said second axes of said reflected beamare perpendicular to one another.
 4. The method of claim 3 wherein saidfirst and said second axes of said reflected beam are the horizontal andthe vertical axes.